Yep, the 5 post rule is only to get access to viewing photos. Help is available from post 1!
Like Wolf said, much more info is needed to get accurate advice.
Tank size, how long set-up, filtration, water change regime, ammonia, nitrIte, nitrAte etc.
As far as the floating fungus is concerned, my best guess would be overfeeding and leftover pellets rotting in the tank. Followed by the resulting ammonia poisoning killing your fish.